My previous U.S. Pat. No. 4,030,556 describes a miniature impact tool that is particularly suited for applications such as engraving, chipping, die making, dental and orthopedic surgery, sculpting, carving, riveting, etc. This is a hand-held impact tool in which rotary motion is converted to linear motion wherein intermittent force is applied to a striker causing it to impact on (contact) a chisel tool held in contact with a workpiece. A drive portion of the miniature tool converts rotary motion to linear motion by means of a cam interface. A spring and plunger arrangement are used to provide the intermittent force which is delivered to a striker that contacts a chisel tool holder. Due to the compressive force of the spring, the striker will provide a sharp blow to the tool holder causing the tool to chip or carve or otherwise impact on the intended workpiece. This cycle is continually repeated as the cam is caused to rotate against a bearing surface connected to the striker.
The entire content of U.S. Pat. No. 4,030,556 is incorporated herein by reference. Pertinent portions thereof will also be reviewed in the description of the preferred embodiments of this invention.
The present invention is based on a recognition of potential wear problems in selective portions of the miniature impact tool of my previous U.S. Pat. No. 4,030,556 . Based on my experimentation and use of this impact tool, I have found that the action of the cam against a needle-bearing at an above-the-centerline point can cause a slight "cocking" of the striker-bearing assembly. This allows the bearing assembly to rise so as to sometimes touch the drive shaft. When repeated for a long period of time, this can provide excessive wear of the drive shaft.
I have also found that the striker tends to move in transverse directions during its longitudinal back and forth movement. These slight departures from movement back and forth along a single longitudinal axis can cause increased friction between the striker and its top and bottom adjoining surfaces, as well as between the striker and its adjoining right and left (side) surfaces. The result is increased friction and less efficiency since not all of the force impacted to the striker by the plunger will then be delivered to the cutting tool.
I have also modified my miniature impact tool by designing the chisel-holding end of the tool to accept a collet, where the collet can have different shapes so as to accept chisels of different cross sectional shapes including round, rectangular, and square shapes.
Accordingly, it is a primary object of this invention to provide an improved miniature impact tool of the general type described in my previous U.S. Pat. No. 4,030,566 where reduced weal and increased efficiency results.
It is another object of this invention to provide an improved tool of the general type described in my previous U.S. Pat. No. 4,030,556 in which chisel tools of varying shape can be easily accepted and wherein increased tool efficiency results.
It is another object of this invention to provide an improved tool of the type described in my previous U.S. Pat. No. 4,030,556 in which the features of compactness, light weight, and ability to be hand-held are maintained while providing a more versatile and efficient tool having long life.